1. Field of the Invention
This invention relates to the field of computer system security for preventing unwanted intrusion into a computer system.
2. Background of the Invention
The vast amount of data and information stored in and processed by computers makes them obvious targets for corporate spies and other information thieves. Unfortunately, computers generally are susceptible to security breaches. An ability of a bus coupling a host computer to one or more peripherals to use a direct memory access (DMA) engine to directly read from and write to the host computer's physical memory locations exacerbates the problem. For example, a rogue device can be tapped into the network and can use the DMA engine to obtain massive amounts of data from the host and its peripherals. A bus with this ability to use a host DMA engine is described in U.S. Provisional Applications Ser. Nos. 60/006,431; 60/011,320; and 60/013,302, filed on Nov. 10, 1995, Feb. 8, 1996, and Mar. 8, 1996, respectively. Since peripherals attached to such a bus may be several meters away from the host computer, an unwanted attachment of a rogue device to the bus which could monitor data traffic on the bus and directly access host memory could go unnoticed by legitimate system users.
Conventionally, an addition of security features to a modern, high-performance computer system necessitated incurring substantial costs, especially in order to avoid causing diminished system performance. There is a need, therefore, for a reliable, low-cost security system to prevent unwanted intrusions into a computer system. Optimally, the system should not affect system performance.